1. Technical Field
The invention is concerned with fabrication of products containing sol-gel-produced high-silica glass. Optical fiber and a wide variety of other products are contemplated.
2. Terminology
Terms of critical meaning to the disclosure are defined.
Sol--A dispersion of particles suspended in a suspension liquid--generally of silica-containing particles in water. Ethyl alcohol is a commonly used non-aqueous suspension liquid. (For, these purposes, minor inclusions in the suspension medium, e.g. for modifying characteristics of the resulting gel, and for controlling the gelation process but not retained in the gel, are ignored.)
High-Silica Glass--Glass composed primarily of SiO.sub.2. Minor ingredients do not ordinarily exceed a total of 5 wt %.
Admixed Sol--Sol prepared by mixing already-formed particles with suspension liquid. The gelled product is here referred to as an "admixed gel". (The conventionally used term, "colloidal", sometimes used in the literature to describe an "admixed gel" is avoided.)
Fumed Silica--Particulate SiO.sub.2 prepared by flame hydrolysis of an appropriate silicon compound, e.g. of SiCl.sub.4, generally using an oxyhydrogen torch. The sol used in the experimental work reported was an aqueous suspension of this form of admixed silica.
Precipitate Sol--As distinguished from an admixed silica sol, a precipitate sol is produced by liquid state reaction within the suspension liquid, for example, of a metalorganic precursor in water. The gelled product is sometimes known as a "polymer gel". The inventive teaching is not applied to precipitate sol.
Gel--A sol which has been gelled so as to be essentially non-fluid. Use of the term does not require total gelation, but only attainment of sufficient structural integrity for needed shape retention.
Overcladding--This refers to a tubular region which, as encompassing a core rod, forms the composite preform from which optical fiber is drawn. A type of overcladding in commercial use is a pore-free self-supporting tube. Alternatives include "direct overcladding", in which a still-porous tube is sintered in situ, to shrink and form a unitary body with the encompassed core rod.